Project 2 (P2). Genetic modifiers of atherosclerosis and foam cell lipid droplet metabolism Jonathan Smith, Ph.D., Project Leader Project Summary/Abstract Heart disease is the number one killer of men and women in the United States. Although the incidence of cardiovascular disease deaths has declined, it still accounts for ~1 out of every 3 deaths. Coronary artery disease (CAD) due to atherosclerosis was responsible for most of these deaths. Despite increased knowledge about CAD risk factors and the availably of drugs to treat them, the CAD problem has not been solved. Large human genome wide association studies have identified many common genetic variants associated with CAD, but only a small fraction of the heritable risk has been discovered. Here we propose to perform mouse genetic and genomic studies to identify atherosclerosis modifier genes and genetic modifiers of foam cell lipid droplet metabolism, yielding insights into the mechanisms that regulate these pathways. These findings may lead to novel drug targets and therapies to prevent or treat CAD. The first aim of the proposed studies involves identifying the responsible genes and genetic variation that give rise to the mouse atherosclerosis susceptibility loci on chromosomes 2 and 17, which we have recently independently replicated. Validation will be performed by allele replacement, the gold standard method to demonstrate a direct causal effect of genetic variation on a phenotype. The second aim of the proposed studies involves the study of an intermediate phenotype that we discovered in atherosclerosis sensitive vs. resistant mice. We found that cholesterol ester stored in lipid droplets of macrophage foam cells is metabolized by autophagy with hydrolysis mediated by lysosomal acid lipase, such that the atherosclerosis sensitive strain has lower rates of flux through this pathway, implying that this pathway is atheroprotective. Thus, we propose to use genetic, genomic, and proteomic studies to identify the genetic variant responsible for this intermediate phenotype, and validate the causal genetic variant via allele replacement. Finally, we will probe whether the antiatherogenic effect of mTOR inhibitors in mice is mediated via an induction of foam cell autophagy.